In a conventional magnetic recording tape cartridge for a video tape recorder, the tape reels contained in the cartridge case are prevented from idle rotation by a tape reel locking mechanism so that the magnetic recording tape wound around the tape reels is not loosened when the cartridge is not being used, and locking of the tape reels is released when the cartridge is mounted in a video tape deck.
FIG. 9 shows a typical example of a conventional tape reel locking mechanism, which comprises a pivotal shaft 7 and a spring bearing member 8 provided in the inner bottom surface of a bottom section 1b of a cartridge case 1 in the rear central portion thereof, and a boss 13 of a tape reel stopper 10 is rotatably engaged with the pivotal shaft 7. The pivotal shaft 7 is further engaged with a central helical portion 11'a of a helical spring 11', one end of which is supported by the spring bearing member 8 and the other is supported by a spring bearing portion of the tape reel stopper 10, the tape reel stopper 10 being rotatingly pressed by the elastic force of the helical spring 11' in a certain direction so that a rotation preventing member 14 of the tape reel stopper 10 is engaged with teeth 5 which are continuously formed along the outer periphery of a lower flange 2b of the tape reel 2 so as to prevent the tape reel 2 from idle rotation when the magnetic recording tape cartridge is not being used. On the other hand, when the magnetic recording tape cartridge is mounted on a video tape deck, the tape reel stopper 10 is forcibly rotated against the helical spring 11' in such a direction that the rotation preventing member 14 is disengaged from the teeth 5, thereby automatically releasing the locking of the tape reels.
Such construction is, however, disadvantageous in employing the helical spring 11'. That is, when assembling the helical spring 11' into the tape reel locking mechanism, both ends thereof should be elastically deformed in a compressed condition followed by engagement of the central helical portion 11'a with the pivotal shaft 7, and thereafter the ends of the helical spring 11' should be brought into contact respectively with the spring bearing member 8 and the tape reel stopper 10 to be supported thereby. Such assembly work is troublesome and should be conducted by hand, and thus the helical spring cannot be automatically assembled into the tape reel locking mechanism. Further, ends of the helical spring 11' of this kind tend to move in the upper and lower directions respectively, leading to deterioration of the spring characteristics and to the apprehension that the helical spring 11' on the assembly line will be sprung out of place by a slight vibration. Still further, a helical spring is generally costly in comparison with a plate spring.